1. Field of the Invention
The present invention relates to a traction control system for a motor vehicle and, in particular, to a traction control system in which a slip value of a driving wheel is controlled by employing an estimated friction coefficient of a road surface.
2. Description of Related Art
A traction control system for a motor vehicle detects a slip value of a driving wheel and controls an output of an engine and braking force so that the slip value of the driving wheel is equal to a predetermined desired slip value. The traction control system is used to prevent a decrease of an acceleration of the vehicle caused by the slip, which is caused by an excessive driving torque of the driving wheel in an accelerating operation and the like.
The traction control system needs to provide the desired slip value, which is determined by a friction coefficient .mu. of the road surface, a vehicle speed an accelerator opening, a steering angle, selection of either a sports and normal mode, or a the like.
The conventional traction control system shown in Japanese Patent Laid-Open Publication No. 60-197434 estimates the friction coefficient .mu. of the road surface based on the acceleration value of the driven wheel when it is determined that a slip is caused. Therefore, in the conventional traction control system, it is difficult to estimate the friction coefficient .mu. of the road surface accurately based on the slip condition, the running condition of the vehicle and the like.